Among the existing structural toy guns, there is a kind of air gun, wherein an air cylinder and piston module is provided inside the gun body, which is designed especially for children players. Through the movement of the air cylinder and the piston module, the air inside the air cylinder is compressed, and then produces a reverse direction of pressure power to fire bullets, but there are some problems existing as below:    1. unable to fire continuously: in each compression from the air cylinder and the piston module, it can only allow to fire a bullet each time. So, every time after firing a bullet, the air inside the cylinder must be compressed again for another shot action, so it cannot fire continuously.    2. the firing effect is unsatisfactory: the reverse direction of pressure power compressed by the air cylinder and the piston module is not large, so the firing effect is unsatisfactory.